Such a transducer is described in DE-A-3 510 341 (U.S. Pat. No. 4,639,904).
Cup-shaped or planar transducers as described in DE-A-3 119 295 (U.S. Pat. No. 4,526,168), in which the ultrasonic shock waves are focussed by electronic or acoustic means, are used in medicine for disintegrating concretions in body cavities, or for destroying tissue and the like.
In such transducers, it is always attempted to concentrate the ultrasonic shock waves most accurately at a geometrical or acoustic site or focus, in order to obtain the necessary energy density for the treatment in hand. For the application of the ultrasonic shock waves, said focus of the transducer is centered on the object to be destroyed.
Such ultrasonic shock waves are usually satisfactory when they are first applied. For example, there is a high probability of a sufficiently large concretion being destroyed when it is first treated. Frequently, however, a number of smaller fragments of the concretion are left and these in turn must be destroyed, at considerable expense, since each fragment must be individually treated.